This invention relates to a process for the recovery of oleophilic surfaced mineral particles from gangue by attracting said mineral particles to the surface of an oleophilic sieve. More particularly, this invention relates to a process for the separation and recovery of oleophilic surfaced mineral particles from gangue utilizing an endless oleophilic conveyor sieve operating in conjunction with specified separation and recovery means.
Industrial nations are constantly increasing their metal consumption and the known supply of metal, and particularly copper, lead and zinc, is shrinking. In a few years, the metal industry may not be able to supply the world needs. Similarly, the supply of previous metals and minerals is shrinking. There are, however, still large quantities of minerals and metals in very low grade ore that have been heretofore untouched because of the difficulty in recovering the valuable minerals and metals from the other solid materials, referred to as gangue, which are of little value.
In the low grade ore, the desired minerals many times appear only as just a few specks mixed with other minerals and solids, and a great amount of material must be handled to recover the small amount of desired mineral or metal. Any process for recovery of the desired minerals from low grade ore should involve as few handling steps as possible.
In addition, there has been difficulty in developing processes that can detect or select the small amount of mineral from the large amount of solids of little value generally termed gangue. This operation known as ore dressing or concentration generally involves comminution or fragmentation of the ore to small size to permit easy separation of the different kinds of solids, followed by one or more sorting operations designed to distinguish and separate the valuable mineral particles from the rest. In the past, the sorting has generally been accomplished by techniques, such as, for example, those based on gravity, magnetism, chemical attraction or reaction.
The gravity separation processes depend upon the different rates of fall through water and are patterned after the simple panning technique where the particles are swirled with water in a shallow conical dish with the effect that the dense particles stratify in the bottom while the lighter mineral, being more buoyant, remain partly suspended and can be decanted with water from time to time. The modern successors to the panning technique use more complicated steps and equipment, but the process is still limited by difficulty of obtaining particles of the right size, interference with walls and bottom of the containing vessels, and the like.
The magnetic separation process can be used for separating only a few minerals. The most obvious case is that of the ferromagnetic magnetite and minerals that can be chemically altered to become magnetic. Such separators work efficiently only if the material is presented in rather a thin layer only a few particles deep. Consequently, the design of a high capacity plant for use with fine material at reasonable cost is scarcely practicable.
The contact method of concentrating ore by causing its adhesion to a solid wall, such as a greased table, a greased solid belt, or the interior solid surface of a drum, is taught in U.S. Pat. Nos. 1,448,928 and 3,399,765. However, this method works efficiently only if the ore mixture to be separated is presented to the wall in rather a thin layer which is at most a few particles deep. Such a method requires an inordinately large solid surface area to affect a high rate of ore separation. Consequently, the design of a high capacity plant at a reasonable cost for that process is impracticable.
Froth flotation is probably the more desirable of the sorting processes as it operates through the sensitive surface properties of the individual minerals. It is generally applicable to very fine concentrates and can distinguish, not only ore mineral from gangue, but one mineral from another. Briefly, conditions are arranged so that when a mixture is agitated and air bubbles are blown through it, certain minerals attach themselves to the bubbles and are floated out of a froth which is skimmed off and discharged of its mineral burden. In many cases, the surface properties of the ore and gangue minerals vary within too narrow a range to be useful for effective separation, and, as a result, certain organic compounds called collectors are added to bring about more selective adsorbtion. The main type of collectors are organic acids, their salts, organic bases and oils, such as kerosene, creosotes, diesel or fuel oils. To be effective, these processes generally require strict control over particle size, of pH and the addition of many additives, such as conditioners, wetting agents, frothing agents, which add greatly to the cost, particularly when treating large quantities of ore. In addition, the technique requires that the minerals be ground to very fine particles before an effective separation can be accomplished.